This invention relates to a disc cartridge for a minidisc (MD) or the like having a disc-like medium such as an optical disc or the like received therein, and more particularly to such a disc cartridge of a three-piece structure wherein an upper plate and a lower plate are joined to each other through a center frame interposedly arranged therebetween.
A disc cartridge which has been conventionally known in the art is generally constructed in such a manner as shown in FIG. 1 by way of example. More particularly, a conventional disc cartridge generally designated at reference numeral 100 in FIG. 1 includes a lower plate 110 and an upper plate 150 securely joined to each other by means of screws 186 while being superposed on each other and having a disc-like medium 170 received therebetween, resulting in being constructed into a two-piece structure.
The lower plate 110 and upper plate 150 of the disc cartridge 100 are respectively formed with openings 111 and 151 through which a recording/reproducing head of an information recording/reproducing apparatus or the like is inserted into the disc cartridge to carry out recording/reproducing of data with respect to the disc-like medium 170. The disc cartridge 100 includes a shutter 180 of a substantially U-shape in section arranged so as to render the openings 111 and 151 open when the head or the like is inserted therethrough and closed otherwise. The shutter 180 is provided on both ends thereof with engagements 181, through which the shutter 180 is engaged with both upper and lower plates 150 and 110. The lower plate 110 is provided thereon with a shutter lock 153 for locking the shutter 180 at a position at which the shutter 180 closes the openings 111 and 151.
Also, the upper and lower plates 150 and 110 are formed on a side surface thereof with depressions or recesses 152 and 112, which cooperate with each other to provide a labeling region when both plates are joined together.
The upper plate 150 is provided thereon with a shutter slide region 153 including the opening 151. The shutter slide region 153 is formed into a reduced thickness so that an outer surface of the shutter 180 and that of the upper plate 150 are flush with each other when the shutter is mounted on the upper and lower plates 150 and 110. This is also true of the lower plate 110.
The upper plate 150 is provided with a gate 154 for molding thereof, which is located in the shutter slide region 153. A failure in cutting of the gate 154 leads to occurrence of burrs. This would deteriorate satisfactory sliding of the shutter 180 and leads to occurrence of shavings, to thereby causes dropout. In order to avoid the possible problem, the gate 154 is formed in a manner to be depressed from an outer surface of the shutter slide region 153. Also, in order to ensure satisfactory flowing of resin during molding of the upper plate 150, the upper plate 150 is formed at a portion of an inner surface thereof positionally corresponding to the gate 154 with a projection-like cold slug well (not shown).
It is generally required that the disc cartridge 100 is formed so as to exhibit rigidity or durability sufficient to ensure outdoor use thereof. Such an increase in rigidity would be attained by increasing a thickness of the upper and lower plates 150 and 110. Unfortunately, this causes occurrence of a sink mark, leading to a deterioration in appearance of the disc cartridge.
In view of the foregoing, a disc cartridge which is constructed into such a three-piece structure as shown in FIG. 2 is proposed as disclosed in Japanese Patent Application Laid-Open Publication No. 78478/1989. More specifically, the disc cartridge generally designated at reference numeral 200 includes an upper plate 250, a lower plate 210, and a center frame 230 interposedly arranged between the upper plate 250 and the lower plate 210, resulting in exhibiting increased rigidity.
Thus, the conventional disc cartridge is constructed into a three-piece structure when it is required to exhibit increased rigidity and massive properties. Otherwise, it is constructed into a two-piece structure.
In the conventional disc cartridge 200 shown in FIG. 2, the center frame 230 is provided on a peripheral portion of each of upper and lower surfaces thereof with a stepped portion 231 of an L-shape in section, in which a side surface of each of the upper plate 250 and lower plate 210 is fitted, to thereby permit each of the upper and lower surfaces of the disc cartridge assembled to be flat. Unfortunately, such construction causes a boundary line between the center frame 230 and each of the upper and lower plates 250 and 210 to be formed on each of the upper and lower surfaces of the disc cartridge assembled. Such a boundary line causes a difference in level, often leading to a failure in smooth loading and unloading of the disc cartridge with respect to an information recording/reproducing apparatus.
In the conventional disc cartridge shown in FIG. 1, as described above, the labeling region to which a label is applied includes a mating line defined between the upper plate 150 and the lower plate 110 as well as the depressions 152 and 112 thereof, to thereby often fail to be flat and tend to be stepped. Formation of such a stepped portion leads to a failure in satisfactory labeling and causes a label adhered to the labeling region to be easily removed therefrom.
The disc cartridge of a three-piece structure shown in FIG. 2 eliminates the above-described problem relating to labeling; because the upper plate 250 and lower plate 210 are fitted at the outer periphery thereof in the stepped portions 231 formed on the inner periphery of the upper and lower surfaces of the center frame 230, to thereby render a side surface of the disc cartridge 200 free from any mating line. Instead, such construction of the disc cartridge causes a mating line between the center frame 230 and the plates to be defined in proximity to an outer edge of the upper and lower surfaces of the disc cartridge. This often fails in proper positioning of the disc cartridge in the information recording/reproducing apparatus and causes the disc cartridge to be caught in the apparatus.
In general, the upper and lower plates are made of polycarbonate (PC) resin, to thereby exhibit satisfactory sliding properties. However, the center frame is required to be made of a material increased in rigidity. This generally causes the center frame to be made of a material different from that of the upper and lower plates, resulting in the center frame being deteriorated in sliding properties depending on the material. When the center frame fails to exhibit satisfactory sliding properties, contacting of the shutter with at least a part of the center frame during sliding movement thereof causes the shutter to be deteriorated in operation. In order to improve a design or appearance of the disc cartridge, it is often practiced to make the upper and lower plates of a transparent material to permit the center frame to be externally visible and color the center frame by painting or plating. Contacting of the shutter with the center frame during the sliding movement causes a colored layer formed on the center frame to be peeled therefrom as well as the above-described deterioration in operation of the shutter.
In order to keep the shutter from being in contact with the center frame to eliminate the above-discussed problem, it would be considered that the center frame is formed into a substantially C-shape, resulting in being excluded or removed from a location in proximity to a region of sliding of the shutter. However, this fails to increase rigidity of the center frame.
Such exclusion of the center frame from the region of sliding of the shutter reduces strength of the upper and lower plates, leading to cracking or breakage of the disc cartridge, because a portion of each of the upper and lower plates positioned on an outside of the opening and in proximity to the region of sliding of the shutter cannot be formed into a sufficient thickness. Likewise, this causes occurrence of an interstice, resulting in dust possibly entering the disc cartridge through the interstice.
In the disc cartridge 200 shown in FIG. 2, an attempt to provide the upper plate 250 with a gate for molding as in the disc cartridge 100 of FIG. 1 would be considered. Such an attempt requires to provide a projection-like basin on an inner surface of the upper plate positionally corresponding to the gate. This requires that the center frame 230 is provided with a depression or recess in order to prevent any interference between the basin and the center frame. Unfortunately, such a recess of the center frame is externally observed or visible, leading to a deterioration in appearance of the disc cartridge and a reduction in commercial value thereof, when the upper plate 250 is made of a transparent or semitransparent material.
In general, assembling of a disc cartridge or tape cartridge into a completed product is carried out by integrally joining two synthetic members such as upper and lower casing or plate members to each other using any suitable fastening or fixing means. In this instance, it is proposed that the casing members are provided on an outer surface thereof with rough ruggedness and fine ruggedness, to thereby prevent the cartridge from dropping from the hand by mistake or provide the cartridge with a stereoscopic feeling due to irregular reflection of light thereon, as disclosed in Japanese Utility Model Publication No. 4469/1994. Also, it is proposed that the casing members each are formed on the outer surface thereof with ruggedness which permits incident light to be reflected thereon in various directions, to thereby keep an inside of the cartridge out of sight or permit the cartridge to optically exhibit a rainbow phenomenon, leading to an increase in commercial value of the cartridge, as disclosed in Japanese Utility Model Application Laid-Open Publication No. 156070/1986.
The conventional cartridge thus formed thereon with ruggedness fails to exhibit such intended or expected advantages of the ruggedness as described above when it is dropped or rubbed by mistake during loading/unloading thereof or handling thereof. Also, the ruggedness causes an inside of the cartridge to be out of sight although it is made of a material transparent sufficiently to permit the inside to be externally visible. Further, when the ruggedness is undesirably formed into a lens-like configuration, the inside is caused to be distortedly visible.